1. Field of the Invention
The present invention generally relates to an image forming apparatus such as a copier, a printer, a facsimile machine, or a multifunction machine including at least two of these functions, and a method of cooling the apparatus.
2. Discussion of the Background Art
In general, electrophotographic image forming apparatuses, such as copiers, printers, facsimile machines, or multifunction devices including at least two of those functions, etc., include an exposure device to direct writing light onto an image carrier so as to form an electrostatic latent image thereon, a development device to develop the latent image with developer, a transfer unit to transfer the developed image (toner image) onto a sheet of recording media, and a fixing device to fix the toner image on the sheet. These devices include driving motors, heaters, and the like, all of which act as heat generators that generate heat. When the temperature inside the image forming apparatus is increased beyond a certain point due to the heat generated by those heat generators, the toner used to develop images might coagulate, resulting in substandard images.
Therefore, such image forming apparatuses typically include air-cooling devices composed of an air-cooling fan and an air duct, and guide external air sucked in by the air-cooling fan onto the hot portions of the apparatus through the air duct to cool the hot portions.
However, at present, the amount of space available between the various components inside the image forming apparatus continues to shrink due to increasing demand for more compact image forming apparatuses, and accordingly it is difficult to secure sufficient space for installing the air duct to cool the hot portions in the apparatus.
In view of the foregoing, certain known image forming apparatuses use a liquid-cooling device that circulate cooling liquid to cool the hot portion. The liquid-cooling device includes a heat receiving portion where the cooling liquid receives heat from the hot portion, a radiator serving as a heat releaser to release heat from the cooling liquid, and a cooling fan serving as an airflow generator to cool the radiator. The cooling liquid is circulated through a circulation pipe between the heat receiving portion and the radiator by a pump. The cooling liquid draws heat from the hot portion in the heat receiving portion and then is transported to the radiator. The radiator is cooled by the air sucked in by the cooing fan to enhance the heat release efficiency, and the air heated by the radiator is exhausted through an exhaust duct.
The cooling efficiency of the liquid-cooling device is higher than that of typical air-cooling devices. In addition, because the circulation pipe for the cooling liquid can be smaller than the air duct, installing the circulation pipe in a limited space is easier. Therefore, the liquid-cooling device is preferable to cool, for example, a development device in which space between the components is smaller, an area around the fixing device that generates a relatively large amount of heat, and sheets on which images are fixed.
Because the cost of the liquid-cooing device is higher, usage of the liquid-cooling devices is limited to the above-described portions, and the air-cooling devices are used instead in such portions that can be cooled sufficiently by the air-cooling device and have sufficient space for installing the air duct.
However, the above-described known image forming apparatus including both the air-cooling device and the liquid-cooling device has a drawback in that, because separate air-suction ducts each provided with an air-suction port are necessary for the cooling fan of the air-cooling device and that of the liquid-cooling device, the number of components increases, resulting in an increases in the size as well as the cost of the apparatus.
Therefore, there is a need to achieve efficient cooling of the hot portions in compact image forming apparatuses without increasing the cost, which known approaches fail to do.